Anderson, who is ranked 32nd, served 11 aces and broke the third-seeded Melzer three times to set up a semi-final against Juan Martin Del Potro of Argentina.

"I have to admit that the better player won today," said Melzer, who did not get a break point. "I had no idea where he was going to serve. We had maybe five rallies in the whole match so I could not find any rhythm."

Anderson, who won his maiden title in his native Johannesburg in February, will play his third semi-final of the season.

The 15th-ranked Del Potro beat Tommy Haas of Germany 6-2, 6-4 to reach his first semi-final since winning his ninth career title in Estoril, Portugal, in April.

"My form is slowly coming back, it's getting better every day," said Del Potro, who conceded just seven points on serve in the entire match. "I am serving better now than in 2009 but I am still working on my game."

Del Potro said that beating the experienced Haas, who won the event in 2001, was "important for my confidence ... The Davis Cup (final against Spain) is on my mind every day but the important thing now is this tournament and the next match."

Also, qualifier Daniel Brands of Germany beat Belgium's Steve Darcis 6-3, 6-4 to reach his first semi-final of the season. Brands double-faulted on match point and then was broken while leading 5-2 but closed out the match in his next service game.

Brands will face top-seeded Jo-Wilfried Tsonga or Xavier Melisse in the semi-finals.

Results from the fifth day of the ATP tournament on Friday (x denotes seeding):Quarter-finals

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